1. Field of the Invention
The present invention relates, in general, to a temperature controller and heating cable used for electric heating bedding, such as an electric blanket, electric papered floor or electric fomentation device, or warmers and, more particularly, to a controller having a safety device, which can immediately shut off the supply of power when the disconnection, breakage or local overheating of a heating cable occurs while preventing the generation of an induced magnetic field and the leakage of an electric field, in warmers, such as simple bedding or fomentation devices that are operated by allowing a user to simply control a heating temperature to a high or low level without measuring the temperature of a separate heating cable.
2. Description of the Related Art
For the sound sleep of human beings, the surrounding conditions of beds, such as temperature and humidity, are important factors. In typical homes, electric heating bedding or fomentation devices are frequently used to maintain beds at suitable temperatures. Such electric heating bedding or fomentation devices include a heating cable, which generates heat when power is supplied to the heating cable. Therefore, a temperature controller for sensing the temperature of the heating cable and controlling the supply of power according to the sensed temperature is generally provided.
Technology for automatically sensing the temperature of a heating cable, comparing the sensed temperature with a temperature set by a user and controlling the temperature was disclosed in Korean Pat. Application No. 2005-2886 filed by the present applicant. This technology is implemented by inserting a Negative Temperature Coefficient (NTC) thermistor between first and second electrical heating wires and determining whether heat is generated through the use of a signal generated by the NTC thermistor. However, high-grade bedding or fomentation devices for automatically sensing and controlling temperature have relatively high manufacturing costs.
Electric heating bedding or fomentation devices having relatively low manufacturing costs do not have a separate temperature sensing function, but allow a user to personally operate a switch so as to turn on or off power. Such electric heating bedding or fomentation devices are problematic in that, if power is turned on for a long period of time, electrical heating wires are disconnected or an insulating coating is melted, so that a fire may occur. Therefore, a circuit for sensing the temperature of a heating cable including electrical heating wires is generally included in the electric heating bedding or fomentation devices. In order to sense the temperature of the heating cable, a separate temperature sensing wire must be included in the heating cable. In this case, the thickness of the heating cable increases, so that it is inconvenient to produce and use the heating cable.
Accordingly, occasionally, a temperature sensing wire is not included in the heating cable, but a separate temperature sensor is placed near the heating cable to sense temperature. However, in this scheme, since it is difficult to sense that an insulator has melted and first and second electrical heating wires have shorted, or sense that respective electrical heating wires have disconnected, a simpler or more efficient safety device is required.